A part of the background hereof lies in the development of heterojunction bipolar transistors which operate as light-emitting transistors and transistor lasers. Reference can be made for example, to U.S. Pat. Nos. 7,091,082, 7,286,583, 7,354,780, 7,535,034 and 7,693,195; U.S. Patent Application Publication Numbers US2005/0040432, US2005/0054172, US2008/0240173, US2009/0134939, and US2010/0034228; and to PCT International Patent Publication Numbers WO/2005/020287 and WO/2006/093883. Reference can also be made to the following publications: Light-Emitting Transistor: Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-II GaAsSb/InP Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Appl. Phys. Lett. 84, 4792 (2004); Laser Operation Of A Heterojunction Bipolar Light-Emitting Transistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85, 4768 (2004); Microwave Operation And Modulation Of A Transistor Laser, R. Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, 131114 (2005); Room Temperature Continuous Wave Operation Of A Heterojunction Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005); Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 88, 012108 (2006); The Transistor Laser, N. Holonyak and M Feng, Spectrum, IEEE Volume 43, Issue 2, February 2006; Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. Phys. Lett. 88, 063509 (2006); and Collector Current Map Of Gain And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, N. Holonyak, Jr., A. James, and G. Walter, Appl. Phys. Lett. 88, 14508 (2006); Collector Breakdown In The Heterojunction Bipolar Transistor Laser, G. Walter, A. James, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 88, 232105 (2006); High-Speed (/spl ges/1 GHz) Electrical And Optical Adding, Mixing, And Processing Of Square-Wave Signals With A Transistor Laser, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Photonics Technology Letters, IEEE Volume: 18 Issue: 11 (2006); Graded-Base InGaN/GaN Heterojunction Bipolar Light-Emitting Transistors, B. F. Chu-Kung et al., Appl. Phys. Lett. 89, 082108 (2006); Carrier Lifetime And Modulation Bandwidth Of A Quantum Well AlGaAs/InGaP/GaAs/InGaAs Transistor Laser, M. Feng, N. Holonyak, Jr., A. James, K. Cimino, G. Walter, and R. Chan, Appl. Phys. Lett. 89, 113504 (2006); Chirp In A Transistor Laser, Franz-Keldysh Reduction of The Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and M. Feng, Appl. Phys. Lett. 90, 091109 (2007); Photon-Assisted Breakdown, Negative Resistance, And Switching In A Quantum-Well Transistor Laser, A. James, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 90, 152109 (2007); Franz-Keldysh Photon-Assisted Voltage-Operated Switching of a Transistor Laser, A. James, N. Holonyak, M. Feng, and G. Walter, Photonics Technology Letters, IEEE Volume: 19 Issue: 9 (2007); Experimental Determination Of The Effective Minority Carrier Lifetime In The Operation Of A Quantum-Well n-p-n Heterojunction Bipolar Light-Emitting Transistor Of Varying Base Quantum-Well Design And Doping; H. W. Then, M. Feng, N. Holonyak, Jr., and C. H. Wu, Appl. Phys. Lett. 91, 033505 (2007); Charge Control Analysis Of Transistor Laser Operation, M. Feng, N. Holonyak, Jr., H. W. Then, and G. Walter, Appl. Phys. Lett. 91, 053501 (2007); Optical Bandwidth Enhancement By Operation And Modulation Of The First Excited State Of A Transistor Laser, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 183505 (2007); Modulation Of High Current Gain (β>49) Light-Emitting InGaN/GaN Heterojunction Bipolar Transistors, B. F. Chu-Kung, C. H. Wu, G. Walter, M. Feng, N. Holonyak, Jr., T. Chung, J.-H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 91, 232114 (2007); Collector Characteristics And The Differential Optical Gain Of A Quantum-Well Transistor Laser, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 243508 (2007); Transistor Laser With Emission Wavelength at 1544 nm, F. Dixon, M. Feng, N. Holonyak, Jr., Yong Huang, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 93, 021111 (2008); and Optical Bandwidth Enhancement Of Heterojunction Bipolar Transistor Laser Operation With An Auxiliary Base Signal, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 93, 163504 (2008).
Semiconductor light emitting diodes (LEDs) and lasers using direct gap III-V materials, and electron-hole injection and recombination, have over the years led to numerous applications in display and lightwave communications. While semiconductor lasers typically dominate long-distance communication links, fast spontaneous lightwave transmitters can be an attractive solution for short range optical data communications and optical interconnections as their threshold-less operation, high fabrication yield and reduced driver and feedback control complexity significantly reduce the overall cost, form factor and power consumption of transmitters. Coupled with a proper cavity design, such as a resonant cavity, spontaneous light sources emitting at 980 nm have been shown to achieve external quantum efficiencies (ηext) as high at 27% and an emission spectral width as narrow as 5 nm (see J. J. Wierer, D. A. Kellogg, and N. Holonyak, Jr., Appl. Phys. Lett. 74, 926 (1999)). However, the fastest spontaneous light source shown to date (a light emitting diode) employs p-doping as high as 7×1019 cm−3 to achieve a bandwidth of 1.7 GHz (i.e., recombination lifetime of ˜100 ps), at the cost of a reduced internal quantum efficiency to 10% or less (see C. H. Chen, M. Hargis, J. M. Woodall, M. R. Melloch, J. S. Reynolds, E. Yablonovitch and W. Wang, Appl. Phys. Lett. 74, 3140 (1999)). In practice, higher efficiency spontaneous devices such as LEDs or RCLEDs operate with bandwidths that are less than 1 GHz, restricting actual commercial application of spontaneous light transmitters (LEDs and RCLEDs) to less than 1 Gbits/s.
It has previously been proposed that the heterojunction bipolar light emitting transistor (HBLET), which utilizes a high-speed heterojunction bipolar transistor (HBT) structure, could potentially function as a light source with speeds exceeding ten's of GHz (see M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); W. Snodgrass, B. R. Wu, K. Y. Cheng, and M. Feng, IEEE Intl. Electron Devices Meeting (IEDM), pp. 663-666 (2007)). The room temperature, continuous wave operation of a transistor laser further demonstrates that a practical radiative recombination center (i.e., undoped quantum well) can be incorporated in the heavily doped base region of a HBLET (see M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005)). Due to the short base effect of tilted charge population in transistors, the effective minority carrier lifetime in the base region of the HBLETs can be progressively reduced to sub-100 ps by tailoring the doping and incorporating QW(s) (see H. W. Then, M. Feng, N. Holonyak, Jr, and C. H. Wu, “Experimental determination of the effective minority carrier lifetime in the operation of a quantum-well n-p-n heterojunction bipolar light-emitting transistor of varying base quantum-well design and doping,” Appl. Phys. Lett., vol. 91, 033505, 2007; G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr., “4.3 GHz optical bandwidth light emitting transistor,” (submitted to Appl. Phys. Lett.), 2009, supra) In practice, despite the high intrinsic speed of the HBT, the microwave performance of an HBLET is limited by parasitic capacitances, due to factors including extrinsic carrier transport effects and to the need to include light extraction features (such as oxide apertures) not present in traditional high speed HBT devices.
It is among the objects of the present invention to address such limitations of prior devices and techniques, and to improve operation of tilted charge light-emitting devices and techniques, including three terminal light-emitting transistors and two terminal tilted charge light emitters.